The difficulties to obtain convenient monocrystals of the important fungicide RPA 406194 have been overcome by a combination
of solid state 13C NMR, X-ray powder diffraction and molecular modeling. The compound, a 3-aryl tautomer, crystallizes forming infinite
chains of molecules bonded by N–H· · ·N hydrogen bonds, leading to needle-shaped crystals. The tautomerism (equilibrium constant and
energy barrier) of this compound in solution has been studied.